1. Field of the Invention
The present invention relates to a pixel clock generator.
2. Description of the Related Art
An image forming device such as laser printer, digital copier is configured to deflect a laser beam from a semiconductor laser unit by a polygon mirror to scan a photoreceptor drum, form optical spots on the photoreceptor drum, and exposure the drum to form an electrostatic latent image thereon. Such a device generates a phase-locked image clock or a pixel clock for each scan line in accordance with a detection signal indicating the detection of a scan beam with a photo detector. It controls the light emission time of the semiconductor laser unit in line with the phase-locked pixel clock and image data for each line, to control the formation of an electrostatic latent image on the photoreceptor drum.
For example, Japanese Patent No. 4313116 discloses a technique to accurately correct shifts in the pixel positions in main scan direction due to environmental changes. It is to acquire, by preliminary experiment or simulation, characteristic values representing shifts in the dot positions of actual image height from the ideal image height of a scan system and prepare a lookup table based on the characteristic values. Phase shift data is read from the lookup table in line with a temporal fluctuation between horizontal synchronous detection signals to correct the main-scan dot shifts with accuracy by controlling the phase of the pixel clock in accordance with the read phase shift data.